Selective Laser Sintering (SLS) is a powerful laser-based additive manufacturing (interne Verlinkung: https://www.raylase.de/en/applications/additive-manufacturing.html) method that has become an essential tool in modern production. By building parts layer by layer from powdered materials, it opens up new possibilities in terms of design flexibility, process efficiency, and material performance.

As industries shift toward more agile and digital production methods, SLS plays a central role in enabling fast, reliable, and cost-effective part fabrication—both for development and for production. This technology is helping drive innovation across multiple sectors, from engineering and healthcare to mobility and lifestyle.

Selective Laser Sintering (SLS) is a laser technology that uses a laser to selectively fuse powdered thermoplastic materials into solid structures—layer by layer. With this approach, SLS enables the production of highly complex, functional parts directly from digital design data.

A distinction must be made between Selective Laser Sintering (SLS) and Selective Laser Melting (SLM). While both are powder bed fusion technologies, their materials and melting behavior differ significantly:

• SLS works primarily with polymers and sintering, meaning the particles are fused without reaching full melting. This results in lower thermal stress, no need for support structures, and the ability to reuse unsintered powder efficiently.
• SLM, in contrast, is used for metal powders and involves full melting of the material. This requires significantly higher energy input, often necessitates support structures, and typically involves more complex post-processing.

SLS is widely adopted in industries where functional prototypes, lightweight parts, and series-ready polymer components are required. Its support-free nature and material versatility make it a foundational technology in additive manufacturing.

Selective Laser Sintering (SLS) is a powder bed fusion process. The process takes place inside a temperature-controlled build chamber and proceeds layer by layer based on CAD design data.

Step-by-Step Overview of the SLS Process:

1. Preparation of the 3D File
   The starting point is a 3D CAD model that is exported into a printable format (e.g. STL or 3MF) and then broken down into digital layers. Special software is used to optimally align parts in the build space, define the laser tracks and set process parameters such as layer thickness or energy density.
2. Powder Deposition and Preheating
   Inside the build chamber, a recoater blade or roller spreads a thin, even layer of powder across the build platform. The powder is preheated to a temperature just below its melting point to minimize thermal stresses and ensure uniform sintering.
3. Selective Laser Sintering
   A high-power CO₂ laser selectively scans the powder bed, following the cross-section of the current layer. The laser energy fuses the powder particles where needed. The beam is guided by fast and precise laser scanning systems (interne Verlinkung Glossar Laserscanning), enabling high-resolution feature control and precise geometries.
4. Layer-by-Layer Build-Up
   After each layer is sintered, the build platform lowers by a small increment—typically 0.1 mm—and the next powder layer is applied. This process repeats until the entire part is completed. Since the surrounding unsintered powder provides natural support, no additional structures are required, even for overhangs or intricate internal channels.
5. Controlled Cooling Phase
   Once the final layer is complete, the entire build remains in the machine to cool gradually. This slow, passive cooling prevents warping, cracking, and internal stress accumulation—key for maintaining dimensional accuracy and mechanical integrity.
6. Post-Processing and Depowdering
   The cooled part is removed from the powder bed and the powder is removed from the parts using brushes, compressed air or sandblasting. Loose, unsintered powder is recovered – often by automated sieving systems – and can be recycled for future parts. Depending on the application, the part then undergoes optional finishing steps such as dyeing or smoothing.

Thanks to its unique combination of design freedom, functional performance, and support-free manufacturing, Selective Laser Sintering (SLS) is used across a wide range of industries—from product development to regulated sectors such as healthcare and mobility. The technology enables fast iterations, customized geometries, and the production of durable end-use parts directly from digital files.

Selective Laser Sintering offers a unique combination of geometric flexibility, process efficiency, and material variability that sets it apart from traditional manufacturing and other additive methods. Its ability to produce durable, end-use parts without additional tooling makes it an ideal solution for fast-paced product development and small to medium production volumes.

Key benefits of the SLS process include:

• Design freedom: Enables complex geometries, internal channels, and undercuts without the need for support structures.
• Cost efficiency: Reduces tooling costs and shortens lead times, especially for customized or low-volume production.
• Material efficiency: Unsintered powder can often be recycled, minimizing waste.
• High part strength and detail resolution: Produces components with excellent mechanical properties, suitable for functional use.
• Scalability: Suitable for everything from one-off prototypes to series production with consistent quality.

One of the key strengths of Selective Laser Sintering lies in its broad material compatibility. Engineers and designers can choose from a diverse set of polymers tailored to specific performance requirements—ranging from stiff, load-bearing structures to flexible, impact-absorbing parts or components that withstand extreme environments.

The choice of material plays a central role in determining the mechanical properties, thermal stability, surface finish, recyclability, and regulatory compliance of the finished part. Below, we highlight the main categories used in industrial SLS systems.

Rigid Materials

Rigid thermoplastics form the core material group in SLS, used for functional prototypes, tooling, and serial production parts. The most prominent materials are polyamides such as PA12 and PA11, valued for their robustness, precision, and all-around process stability.

These materials provide:

• High tensile and impact strength
• Excellent dimensional stability
• Resistance to chemicals and humidity

Glass-fiber or carbon-fiber reinforced grades further increase stiffness, making them ideal for automotive housings, mechanical brackets, ductwork, and load-bearing fixtures. Their ease of processing, recyclability, and dimensional accuracy make rigid polymers the most widely used class in SLS applications.

Flexible Materials

Flexible materials open up new application spaces for SLS, especially in the field of wearables or cushioning systems. The most common flexible SLS material is thermoplastic polyurethane (TPU).

Engineers select TPU for its:

• Elastic deformation and resilience
• High abrasion and fatigue resistance
• Ability to form soft lattice structures and thin-walled geometries

Modern TPU powders are optimized for low shrinkage and high detail resolution. It enables the creation of components like shoe midsoles, protective gear, gaskets, and medical-grade support devices. In contrast to rigid plastics, these parts can flex, bend, and recover shape without compromising their function. This makes TPU a go-to choice for personalized comfort and movement-driven applications.

High-Performance Polymers

In applications in the aerospace and automotive industries, or in medical devices, mechanical loads, heat and chemical influences often push conventional materials to their limits. Consequently, materials such as PEEK (polyether ether ketone), PEI (polyether imide) and PPSU (polyphenylsulfone) are used for these applications.

Key benefits of these high-performance polymers include:

• High thermal stability (continuous use at up to 250 °C and more)
• Exceptional resistance to chemicals, wear, and mechanical stress
• Biocompatibility and sterilizability for medical applications
• Flame resistance and dimensional stability under load

Despite requiring more advanced equipment and precise process control, these materials enable the production of lightweight, high-strength components that meet the toughest industry standards.